Means to diminish secondary electron emission



June 26, 1934. G. JOBST 1,964,517

MEANS TO DIMINISH SECONDARY ELECTRON EMISSION Original Filed June 2, 1927 s' P f a P I l l I I I 'l ii;

14 5 A Eg /.5

wumuuuu INVENTOR G. JOBST A ORNEY Patented June 26, 1934 PATENT OFFICE MEANS TO DIMINI SH SECONDARY ELECTRON EMISSION Gunther Jobst, Berlin,

Telefunken graphie m. b. 11., tion of Germany Application June 2, 1927, Serial No.

Renewed December 28, 1933.

Germany, assignor to Gesellschai't fiir Drahtlose Tele- Berlin, Germany, a corporaisaass. In Germany June The object or the present invention is a form of construction or arrangement of a thermionic or electron tube so that the emission of secondary electrons by an electrode, for instance, the grid is reduced or completely suppressed.

It is a well-known fact that the grid in thermionic tubes emits electrons when operated at more than average potentials. If the grid potential is higher than, say 100 volts the electron emission assumes rather considerable proportions. Such an emission of secondary electrons involves serious drawbacks in a number of uses of thermionic tubes. For instance, it may happen that, on account of marked emission of secondary electrons, no current is flowing in the outer grid circuit since the direction of the secondary electron current is such that it opposes the primary electron current and just compensates or neutralizes the latter. The result is that what is known as grid modulation telephony, which depends upon the action brought upon the grid and the current flowing therein, becomes impracticable. Another drawback is that on account of secondary electron emission, the production of waves is prevented or that undesired or spurious oscillations are generated. Now, the p p se of the present invention is to provide ways and means whereby appreciable electron emission from the grid is precluded, this being accomplished by the influence of the positive plate potential on the grid, which causes an attraction of the secondary electrons with the result that a secondary electron current ii caused, is prevented.

According to the disclosures of this invention, a conducting body, for instance, in the form of a cage surrounding the grid or else a separate protective grid is provided in close proximity to the main grid, said cage or protective grid being kept at a lower potential or at the same potential as the filament or cathode. One embodiment of the basic idea of the invention consists in an arrangement such that between the control grid and the plate, an additional grid is disposed which is connected directly with the filament so that it is kept at the same potential as the latter.

In the drawing, Fig. 1 is a diagrammatic view oi. the arrangement of the tube elements,

Fig. 2 shows a diagrammatic tube arrangement with a modified form of auxiliary grid,

Fig. 3 is a partial section of a tube embodying my invention,

Fig. 4 is a plan view of Fig. 3,

Fig. 5 shows diagrammatically suitable circuits connected to the elements of the tube, and

Fig. 6 shows a modified form of the tube inFig. 5.

A form of construction as before outlined is diagrammatically illustrated in Fig. 1 showing a section through the axis 01' the electrode arrangement of a thermionic tube. F denotes the filament, G the control grid, P the plate, while the auxiliary grid H is arranged between the control grid G and the plate P, said auxiliary grid being connected directly with the filament by a conducting connection I. It will be understood that the latter connection may be provided either inside the tube as shown in Fig. 6, in which case the construction of the tube must be conveniently chosen, or else outside the tube. The auxiliary grid may be of annular, rod or wound (helical) form.

Another form of construction is illustrated in Fig. 2. In this scheme, the grid is surrounded partly by a conducting cage K which is also connected directly with the filament. However, it has been found to be necessary to envelop only about $4; of the length of the grid by the said cage.

In the tube shown in Figs. 3 and 4 the filament is mounted centrally and surrounding this is the control grid G made of wire into a generally cylindrical form. Close to this grid and surrounding it is the auxiliary grid H made into cylindrical form by a helically wound wire. The plate P may be of any desired shape, that shown being cylindrical, but plates of other form may be used instead.

Fig. 5 shows a circuit arrangement using a tube of this form in which the plate voltage is about 200 volts and that of the main grid about 100 volts, this voltage being supplied by a battery or other source of direct current A. The filament current is supplied by battery B and a sliding contact 0 connected to the auxiliary grid H adjustably engages this battery, whereby voltage of grid H may be made equal to or lower than that of the filament.

In Fig. 6 there is shown a modification of the connection between the cathode F and the auxiliary control electrode H, as shown in Fig. 5, wherein the connection I is disposed within the envelope E, the connection being directly between the electrode H and the cathode F. It is to be understood that the remaining connections of Fig. 6 are similar to those shown in Fig. 5.

While the method and arrangement above described for decreasing or preventing the emission of secondary electrons has been described as applied to the control grid, I do not limit myself to this particular electrode as the auxiliary grid may evidently be used in conjunction with the plate or other electrode of a vacuum tube to prevent emission of secondary electrons therefrom.

Having described my invention and the means which at present I consider preferable for carrying it into effect, it will be understood that I do not limit myself to the means shown but wish to include within the scope of my invention any method and means within the scope of the following claims.

I claim:

1. In a vacuum tube having a source of electrons, a grid, and a plate, an output circuit connected to said grid and plate, means interposed between the grid and plate and spaced from said grid to prevent secondary electrons emitted by the grid due to impact by said first named electrons from moving toward the plate, said means being so constructed that said first electrons reach said plate, and means for maintaining said grid positively charged with respect to the oathode.

2. In an electron discharge tube circuit of the type including a tube provided with a cathode, a highly positive cold electrode, and at least one additional positive cold electrode intermediate the cathode and the first cold electrode, an output circuit to which both the cold electrodes are connected, means for maintaining the said first cold electrode at a positive potential of the order of 200 volts with respect to the cathode, and a grid, connected within the tube to the cathode, disposed between the two cold electrodes for establishing a negative potential field with respect to the cold electrodes to suppress the flow of secondary electrons from one of said cold electrodes in the direction of the other cold electrode.

3. In an electron discharge tube circuit of the type including a tube provided with a cathode, a highly positive cold electrode, and at least one additional positive cold electrode intermediate the cathode and the first cold electrode, an output circuit to which both the cold electrodes are connected, means for applying high positive potentials to said cold electrode of such magnitude with respect to the cathode that electrons emitted from the cathode cause the emission of secondary electrons from at least one of the cold electrodes by impact therewith, and a grid, connected within the tube to the cathode,

4. In an electron discharge tube circuit of the type including a tube provided with a cathode, a highly positive cold electrode, and at least one additional positive cold electrode intermediate the cathode and the first cold electrode, an output circuit to which both the cold electrodes are connected, means for maintaining the said first cold electrode at a positive potential of the or der of 200 volts and the additional cold electrode at a positive potential of the order of 100 volts with respect to the cathode, and a grid, connected within the tube to the cathode, disposed between the two cold electrodes for establishing a negative potential field with respect to the cold electrodes to suppress the flow of secondary electrons from one of said cold electrodes in the direction of the other cold electrode.

5. An electron discharge tube comprising a cathode for emitting primary electrons, a grid electrode and a plate electrode surrounding said cathode, and means for preventing the flow of secondary electrons between said grid and plate electrodes due to primary electron impact thereagainst comprising a conducting cage member which only partly surrounds the grid electrode and is directly connected to the cathode.

6. An electron discharge tube comprising a cathode for emitting primary electrons, a grid electrode and a plate electrode surrounding said cathode, and means for preventing the flow of secondary electrons between said grid and plate electrodes due to primary electron impact thereagainst comprising a conducting cup-shaped member disposed at one end of the electrodes and having a portion extending only partly within the space between grid and plate, said cupshaped member being electrically connected to the cathode.

'7. An electron discharge tube comprising a cathode for emitting primary electrons, a plate electrode at a comparatively high potential surrounding the cathode for collecting the primary electrons, a grid electrode interposed between cathode and plate and maintained at a lower positive potential than the plate, and means for preventing secondary electron emission from grid and plate due to primary electron impact thereagainst comprising a transverse member extending over one end of the grid and connected to the cathode, said member having an annular portion which extends only partly into the space between grid and plate.

disposed between the two cold electrodes for establishing a negative potential field with respect to the cold electrodes to suppress the flow of said secondary electrons from said one cold electrode in the direction of the other cold electrode.

GUNTHER J OBST. 

